Effects of Fuel Injection on Turbulence Enhancement in a Spray-Guided, Gasoline Direct-Injection, Optically Accessible Engine with a High-Pressure Injection System

In this study, the effects of fuel injection on in-cylinder flow under various injection conditions were investigated using particle image velocimetry measurements in a two-cylinder, direct-injection spark-ignition, optically accessible engine with a spray-guided injection system. Various injection timings and pressures were applied to intensify the turbulence of in-cylinder flow. Simple double-injection strategies were used to determine how multiple injections affect in-cylinder flow. The average flow speed, turbulent kinetic energy, and enhancement level were calculated to quantitatively analyze the effects of fuel injection. Fuel injection can supply additional momentum to a cylinder. However, at an early injection timing such as 300° before top dead center, in-cylinder flow development could be disturbed by fuel injection due to piston impingement and interactions between the spray and air. As the injection pressure increased, the in-cylinder flow intensified despite the possibility of increased wall and piston impingement due to lengthened spray penetration. When a double-injection strategy was applied, the second-injection timing was the dominant factor increasing turbulence intensity. As the injection timing was delayed, the effects of fuel injection on in-cylinder flow in the later portion of the compression stroke increased, but with rapid dissipation of momentum during the compression stroke. It would therefore be more effective to apply a multiple-injection strategy and inject a small amount of fuel just before ignition as the final injection to enhance turbulence. However, mixture formation near the spark plug should be considered to increase ignition stability.